selftests/sgx: Add test for TCS page permission changes

Kernel should not allow permission changes on TCS pages. Add test to
confirm this behavior.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/0121ad1b21befb94519072e2c18b89aa5dca00d4.1652137848.git.reinette.chatre@intel.com

Author: rchatre

tools/testing/selftests/sgx/main.c

@@ -121,6 +121,24 @@ static Elf64_Sym *vdso_symtab_get(struct vdso_symtab *symtab, const char *name)
 	return NULL;
 }
 
+/*
+ * Return the offset in the enclave where the TCS segment can be found.
+ * The first RW segment loaded is the TCS.
+ */
+static off_t encl_get_tcs_offset(struct encl *encl)
+{
+	int i;
+
+	for (i = 0; i < encl->nr_segments; i++) {
+		struct encl_segment *seg = &encl->segment_tbl[i];
+
+		if (i == 0 && seg->prot == (PROT_READ | PROT_WRITE))
+			return seg->offset;
+	}
+
+	return -1;
+}
+
 /*
  * Return the offset in the enclave where the data segment can be found.
  * The first RW segment loaded is the TCS, skip that to get info on the
@@ -567,6 +585,59 @@ TEST_F(enclave, pte_permissions)
 	EXPECT_EQ(self->run.exception_addr, 0);
 }
 
+/*
+ * Modifying permissions of TCS page should not be possible.
+ */
+TEST_F(enclave, tcs_permissions)
+{
+	struct sgx_enclave_restrict_permissions ioc;
+	int ret, errno_save;
+
+	ASSERT_TRUE(setup_test_encl(ENCL_HEAP_SIZE_DEFAULT, &self->encl, _metadata));
+
+	memset(&self->run, 0, sizeof(self->run));
+	self->run.tcs = self->encl.encl_base;
+
+	memset(&ioc, 0, sizeof(ioc));
+
+	/*
+	 * Ensure kernel supports needed ioctl() and system supports needed
+	 * commands.
+	 */
+
+	ret = ioctl(self->encl.fd, SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS, &ioc);
+	errno_save = ret == -1 ? errno : 0;
+
+	/*
+	 * Invalid parameters were provided during sanity check,
+	 * expect command to fail.
+	 */
+	ASSERT_EQ(ret, -1);
+
+	/* ret == -1 */
+	if (errno_save == ENOTTY)
+		SKIP(return,
+		     "Kernel does not support SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS ioctl()");
+	else if (errno_save == ENODEV)
+		SKIP(return, "System does not support SGX2");
+
+	/*
+	 * Attempt to make TCS page read-only. This is not allowed and
+	 * should be prevented by the kernel.
+	 */
+	ioc.offset = encl_get_tcs_offset(&self->encl);
+	ioc.length = PAGE_SIZE;
+	ioc.permissions = SGX_SECINFO_R;
+
+	ret = ioctl(self->encl.fd, SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS, &ioc);
+	errno_save = ret == -1 ? errno : 0;
+
+	EXPECT_EQ(ret, -1);
+	EXPECT_EQ(errno_save, EINVAL);
+	EXPECT_EQ(ioc.result, 0);
+	EXPECT_EQ(ioc.count, 0);
+}
+
 /*
  * Enclave page permission test.
  *